1. Field of the Invention
This invention relates to a reflection type optical rotary encoder, and more particularly to a type thereof wherein optical fibers are utilized between the upper surface of a code wheel and light emitting and light receiving elements.
2. Description of Prior Art
FIG. 1 illustrates a typical construction of a prior art rotary encoder wherein a code wheel 2 of a disc shape is mounted on a rotating shaft 1a of a motor 1. On the upper surface 2a of the code wheel 2 are radially disposed sector-shaped reflecting portions 3 equally spaced apart from each other, and nonreflecting portion 4 interposed between the reflecting portions 3. Opposing to the upper surface 2a of the code wheel 2, there are provided a light emitting element 5 and two light receiving elements 6 and 7 which are arranged on both sides of the light emitting element 5. Optical fibers 8, 9 and 10 are extended between the elements 5, 6 and 7 and the code wheel 2, respectively. When the code wheel 2 is rotated, the light emitted from the light emitting element 5 is reflected by the reflecting portions 3, and received in the light receiving elements 6 and 7 thereby providing continuous pulse signals, from which the number of rotations and the rotating direction of the code wheel 2 can be detected.
Heretofore, the first optical fiber 8 that transmits the light emitted from the light emitting element 5, and the second optical fibers 9 and 10 that transmit the light received by the light receiving elements 6 and 7, have end portions facing the code wheel 2 shaped as shown in FIG. 4(b). That is, the ends of the first optical fiber 8 and the second optical fibers 9 and 10 are held in abutment so as to collect light reflected from the code wheel 2 efficiently, and formed into a planar surface extending in parallel with the code wheel 2.
More specifically, the angle K formed between the side surfaces of the second optical fibers 9 and 10 and the planar surface is smaller than 90.degree..
Such an arrangement has entailed a difficulty of the second optical fiber 9 hardly receiving the light G emitted from the first optical fiber 8 and reflected from the upper surface 2a of the code wheel 2 at an angle S.
Furthermore, when a reflection by the end surface of the optical fiber is considered, the light H emitted from the first optical fiber 8 which is reflected from the upper surface of the code wheel 2 reaches the end surface of the second optical fiber 10. At this time, since the refraction index of the optical fiber is different from that of air, one part of the light H is again reflected by the end surface of the second optical fiber 10. Since the incident angle .beta. of this light H at this time is comparatively large, a large part of the light H tends to be reflected by the end surface of the optical fiber 10, thus lowering the light collecting efficiency of the conventional rotary encoder.